JP2014101472A - Uv flexographic ink, and flexographic printing method using the same - Google Patents

Abstract

The present invention provides a UV flexographic ink and a flexographic printing method capable of high-definition printing without printing smear due to plate entanglement.
SOLUTION: At least a polymer, an oligomer and a monomer are blended, the blending ratio of the polymer in the entire UV flexo ink is 4 to 6% by weight, the blending ratio of the oligomer is 25 to 30% by weight, Printing with a blending ratio of 30 to 50% by mass, UV flexo ink with a viscosity of 3000 to 3600 cps at 25 ° C., and an anilox roll with a line number of 600 to 1000 lines / inch and a printing speed of 10 to 80 m / min Perform flexographic printing at speed.
[Selection figure] None

Description

  The present invention relates to a UV flexographic ink used for printing on corrugated cardboard, paper, plastic films, and the like, and a flexographic printing method using the ink.

  Flexographic printing, a type of letterpress printing, is a printing method used for printing on corrugated cardboard, paper, plastic films, etc., and flexographic printing plates made of flexible elastic materials such as rubber and resin, and liquid inks such as water-based ink and UV ink. It is known as an environmentally friendly printing method because it uses no ink and does not use solvent-based ink. In addition, flexographic printing has high accuracy, high-definition printing is possible, and high gradation expression can be printed with high reproducibility.

  In letterpress printing, ink penetrates not only to the top of the convex part of the plate, but also to the side part and concave part of the convex part, and the so-called plate entanglement caused by the ink accumulated in the concave part causes the ink to reach the part where printing is not originally performed. There are cases where printing smudges are transferred.

  In flexographic printing, which is a type of letterpress printing, the flexographic plate is flexible and the convex portions are easily crushed. Therefore, the concave portions of the flexographic plate are easy to contact the anilox roll, and the ink has a low viscosity (400 to 600 cps). Easy to be transferred to flexographic version. In particular, in halftone dot printing in which the area of the convex portion of the flexographic plate is reduced, a phenomenon called dot dipping occurs in which the highlighted convex portion of the plate is immersed in the anilox roll cell. Plate entanglement in which ink enters not only the top of the convex part but also the side part and concave part of the convex part is one of the causes of printing stains.

  The printing design has become finer year by year, and there has been a demand for flexographic printing technology that does not cause printing stains even in fine dot printing.

  As a technique for preventing such plate entanglement in flexographic printing, for example, Patent Document 1 discloses a method of imparting hydrophobicity to the convex surface by bringing a silicone compound or a fluorine compound into contact with the surface during production of the plate. Patent Document 2 discloses a method of starting printing after applying an antifouling agent containing an ink repellent material to the entire flexographic plate and drying it, and then removing the antifouling agent from the convex portion. .

Japanese Patent No. 4548860 JP 2002-292985 A

  However, the methods described in Patent Documents 1 and 2 are still insufficient to prevent plate entanglement in high-definition flexographic printing. In addition, the method described in Patent Document 2 has a problem that it is necessary to apply an antifouling agent and remove it from the convex portion every time printing is performed, and the operation is complicated.

  An object of the present invention is to provide a UV flexographic ink and a flexographic printing method capable of providing a printed matter free from printing stains even in high-definition printing without using a special flexographic plate or adding a new process. Is to provide.

The first of the present invention is a UV flexographic ink for flexographic printing,
At least a polymer, an oligomer and a monomer are blended, the blending ratio of the polymer in the entire UV flexo ink is 4 to 6% by weight, the blending ratio of the oligomer is 25 to 30% by weight, and the blending ratio of the monomer is 30-50% by mass,
The UV flexographic ink has a viscosity at 25 ° C. of 3000 to 3600 cps.

A second aspect of the present invention is a flexographic printing method using UV flexographic ink,
Transferring the UV flexographic ink to an anilox roll;
Transferring the UV flexographic ink from the anilox roll to which the UV flexographic ink has been transferred to a photosensitive resin plate;
A printing method comprising a step of printing a UV flexo ink transferred to the photosensitive resin plate on a printing medium;
The number of lines of the anilox roll is 600 to 1000 lines / inch,
The printing speed at the time of the printing is 10 to 80 m / min.

  According to the present invention, by adjusting the blending ratio and viscosity of the flexographic ink, it is possible to provide a UV flexographic ink that does not cause plate smearing. Further, using the UV flexographic ink, the number of lines of anilox roll and the printing speed can be provided. Is set to an appropriate range, so that plate entanglement can be prevented without greatly reducing the printing speed, and flexographic printing without printing stains can be performed. Therefore, it is possible to provide a beautiful printed material that has been subjected to high-definition printing by the flexographic printing of the present invention.

  The main cause of plate entanglement in flexographic printing is the low viscosity of flexographic ink. However, if the flexographic ink is made to have a high viscosity, the transferability of the ink is deteriorated, so that the printing becomes faint when printing is performed at a high speed. Therefore, conventionally, a flexo ink having a low viscosity (400 to 600 cps) has been used in preference to the printing speed.

  In the present invention, in order to provide a UV flexographic ink free from plate stains, the blending ratio and viscosity of the flexographic ink are adjusted. Further, in printing using the UV flexographic ink, the anilox roll line is used. By adjusting the number and the printing speed, respectively, it is characterized in that the plate entanglement is prevented by using a flexo ink having a higher viscosity than before without significantly reducing the printing speed.

  The UV flexo ink of the present invention comprises at least a polymer, an oligomer, and a monomer, the polymer content in the entire UV flexo ink is 4 to 6% by mass, and the oligomer content is 25 to 30% by mass. And the compounding amount of the monomer is 30 to 50% by mass. Further, the UV flexo ink of the present invention has a viscosity at 25 ° C. of 3000 to 3600 cps (3.0 to 3.6 Pa · s).

  In the present invention, if the blending amounts of the polymer, oligomer, and monomer in the UV flexographic ink are out of the above ranges, it is not preferable because proper printing becomes difficult such as plate entanglement.

  In the present invention, if the viscosity of the UV flexo ink is less than 3000 cps, printing smear due to plate entanglement occurs, and if it exceeds 3600 cps, printing defects such as blurring occur, which is not preferable. In the present invention, the viscosity of the ink is measured with an E-type viscometer at 25 ° C. and 50 rpm (JIS Z 8803).

  In the present invention, the monomer blended in the UV flexographic ink improves the suitability of the cured product (viscosity adjustment, improvement in coating properties) together with the oligomer, and makes the ink itself solvent-free by utilizing its solubility and crosslinkability. Can be

  The monomer used in the present invention is a photopolymerizable monomer that can be polymerized by ultraviolet rays (UV), and known materials are used. Specifically, acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate are used. , Phenoxyethyl acrylate, isodecyl acrylate, n-hexyl acrylate, stearyl acrylate, lauryl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, N, N-diethylaminoethyl acrylate, N, N-dimethylamino acrylate, glycidyl acrylate, allyl acrylate, Monoacrylates such as 2-hydroxyethyl acrylate, benzyl acrylate, cyclohexyl acrylate, 1,3-butanediol diacrylate, 1,6-hexa Diacrylate such as diol diacrylate, polyethylene glycol diacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate, hydroxypivalate ester neopentyl glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol hexaacrylate, etc. Trifunctional or higher acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, lauryl methacrylate, 2-hydroxy methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate and other methacrylates, maleic acid, itacon , Acrylamide, N- methylol acrylamide, diacetone acrylamide, styrene, vinyl toluene, vinyl acetate, acrylonitrile, diallyl phthalate, and the like.

  The oligomer and polymer used in the present invention are the main components in the UV curable composition and affect the physical properties (hardness, adhesion, electrical properties) after curing. In the present invention, the molecular weight is 10,000 or more as a polymer, and less than 10,000 as an oligomer.

  Examples of the oligomer and polymer used in the present invention include polyester acrylate, polyepoxy acrylate, polyurethane acrylate, polyether acrylate, polybutadiene acrylate, polysilicon acrylate, a combination of polyene and polythiol, polymelamine acrylate, and polyalkyd acrylate.

  More specifically, the polyester acrylate includes an acrylate having a hydroxyl group such as 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate, phthalic acid, adipic acid, maleic acid, trimellitic acid, itaconic acid, and succinic acid. , Ester compounds of polybasic acids such as alkenyl acids, or acrylic acid, methacrylic acid and ethylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, trimethylolpropane, dipropylene glycol, polyethylene glycol, Examples thereof include polyhydric alcohols such as pentaerythritol and dipentaerythritol, and polymers of ester compounds based on the above-described polybasic acids.

  Examples of the polyepoxy acrylate include a reaction product of a polymer of bisphenol A and epichlorohydrin, a polymer of phenol novolac and epichlorohydrin, and acrylic acid or methacrylic acid.

  Examples of the polyurethane acrylate include tolylene diisocyanate, tolidine diisocyanate, xylylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, tetramethylxylene diisocyanate. Polymer of urethane compound of isocyanate group-containing compound such as lysine ester triisocyanate and hydroxyacrylate such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, glycidol methacrylate, pentaerythritol triacrylate Is mentioned.

  Examples of the polyether acrylate include a reaction product of ethylene oxide ring-opening polymer and acrylic acid or methacrylic acid.

  Examples of the polybutadiene acrylate include urethane compounds of acrylate and isocyanate compounds having liquid polybutadiene and hydroxyl groups, ester compounds of maleated polybutadiene and acrylate having hydroxyl groups, epoxy ester compounds of liquid polybutadiene having carboxylic groups and glycidyl acrylate, and epoxidation. Polymers such as ester compounds of polybutadiene and acrylic acid are listed.

  Examples of the polysilicon acrylate include polymers such as acrylic silane such as methacryloxypropylmethyldimethoxysilane and acryloxypropylmethyldimethoxysilane, methacrylic silane, acryloxypropyldimethylpolysiloxane, and methacryloxypropylphenylmethylpolysiloxane.

  Examples of the combination of polyene and polythiol include diarylidene pentaerythritol, reaction products of allyl alcohol and polyhydric alcohols such as ethylene glycol and trimethylolpropane and polyvalent isocyanates such as 2,6-tolylene diisocyanate. A combination of polyene and thiol such as polyethylene disulfide or polyethyl ether disulfide can be mentioned.

  In addition to the monomers, oligomers, and polymers described above, the UV flexo ink used in the present invention is blended with pigments and additives as appropriate.

  A photoinitiator is mentioned as an additive used for UV flexographic ink. The photoinitiator has an action of absorbing ultraviolet rays having a wavelength of 200 to 450 nm, and is also called a sensitizer. It is required to efficiently absorb and activate the ultraviolet rays emitted from the UV irradiation apparatus and to have a fast curing speed of the ink containing such a photoinitiator. In the present invention, known materials are used. For example, acetophenone, p-tert-butyltrichloroacetophenone, p-tert-butyldichloroacetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, etc. Acetophenones, benzophenone, Michler's ketone, benzyl, benzoin, benzoin methyl ether and benzoin ethyl ether, benzoin alkyl ethers such as benzoin butyl ether and benzoin isopropyl ether, benzyl dimethyl ketal, benzoyl benzoate, tetramethyl thiuram monosulfide and thiobenzoic acid S- Sulfur compounds such as phenyl, thioxan, 2-chlorothioxanthone, 2-methylthioxanthone, 9,10-anthraquino Quinone derivatives such as and camphorquinone, 3-ketocoumarin, aryl diazonium salt, aryl iodonium salts, arylsulfonium salts, sulfonyl acetophenone, and bis imidazole.

  As other additives, a dispersant, an antifoaming agent, a lubricant and the like are used as necessary.

  As pigments, pigments blended in conventional UV flexographic inks, such as black carbon black, white titanium oxide or titanium white, red brilliant carmine 6C or lake C, yellow diazo yellow, green phthalocyanine green, blue Phthalocyanine blue, purple methyl violet lake and dioxazine violet are used.

  The flexographic printing method of the present invention is a flexographic printing method using the above-mentioned specific UV flexographic ink, a step of transferring the UV flexographic ink to an anilox roll, and a UV flexographic ink is exposed from the anilox roll to which the UV flexographic ink has been transferred. A step of transferring to the photosensitive resin plate, and a step of printing the UV flexographic ink transferred to the photosensitive resin plate on the substrate.

  In the flexographic printing method of the present invention, an anilox roll having a line number of 600 to 1000 lines / inch is used. If the number of anilox rolls is less than 600 lines / inch, the shape of the cell is large and plate entanglement tends to occur. On the other hand, if the number of lines exceeds 1000 lines / inch, the amount of ink transferred from the anilox roll to the flexographic plate is small, and the printing density becomes low. The cell shape of the anilox roll includes a honeycomb shape, a diamond shape, and a helical shape, and any of them can be used in the present invention.

  As the flexographic plate of the present invention, a plate used for general UV flexographic printing can be used. For example, a general-purpose photosensitive resin plate can be used.

  In the flexographic printing method of the present invention, the printing speed is set to 10 to 80 m / min. If the printing speed is less than 10 m / min, the printing speed is slow and the printing efficiency is poor. On the other hand, if the printing speed exceeds 80 m / min, the transferability of the ink from the flexographic plate to the printing material is lowered, and the printing is blurred.

  In the present invention, the printing apparatus, the substrate, and the printing conditions are not particularly limited as long as the above requirements for the viscosity of the flexographic ink and the amount of the oligomer, the number of anilox rolls, and the printing speed are satisfied. Therefore, the flexographic printing method of the present invention can be carried out using the conventional printing apparatus and the printing material as they are.

  Various types of UV flexographic inks with the blending amounts shown in Table 1 are prepared, and using a center impression drum type UV flexographic printing machine (KPG: KPG250), the width is 133 mm, the thickness is 390 μm, and the thickness is 400 μm. Is a laminate of 500 m (layer structure: LDPE film / milk white LDPE / LDPE / deposited PET film / LLDPE film / PE film), 5 pieces for each of two thicknesses, a total of 10 pieces (total 5000 m) for flexographic printing went. As the anilox roll, plastic square cells having a honeycomb shape and the number of lines of 600 lines / inch, 800 lines / inch, and 1000 lines / inch were used. Further, a photosensitive resin plate manufactured by DuPont was used as the flexographic plate, and printing speeds were 10 m / min, 80 m / min, and 150 m / min.

The obtained printed matter and the flexographic plate were visually inspected, and portions that were considered to be defective in printing were observed with a loupe or a magnifier. The results are shown in Table 2. The evaluation criteria are as follows.
Plate entanglement: “X” when ink was accumulated in the concave portion of the flexographic plate, and “◯” when there was no concave portion where the ink was accumulated in the flexographic plate.
Print stain: “X” when a portion of the printed material that was not covered with ink was printed, and “B” when there was no such phenomenon in the entire printed material.

  In Examples 1 and 2 and Comparative Examples 4 to 7, ink was faint at a printing speed of 150 m / min, and proper printing could not be performed. Further, in Comparative Example 8, the ink was faint at any printing speed, and proper printing could not be performed. Note that there was no difference in printing due to the difference in thickness of the laminate fabric.

Claims (2)

UV flexographic ink for flexographic printing,
At least a polymer, an oligomer and a monomer are blended, the blending ratio of the polymer in the entire UV flexo ink is 4 to 6% by weight, the blending ratio of the oligomer is 25 to 30% by weight, and the blending ratio of the monomer is 30-50% by mass,
The UV flexographic ink, wherein the UV flexographic ink has a viscosity of 3000 to 3600 cps at 25 ° C. A flexographic printing method using the UV flexographic ink according to claim 1,
Transferring the UV flexographic ink to an anilox roll;
Transferring the UV flexographic ink from the anilox roll to which the UV flexographic ink has been transferred to a photosensitive resin plate;
A printing method comprising a step of printing a UV flexo ink transferred to the photosensitive resin plate on a printing medium;
The number of lines of the anilox roll is 600 to 1000 lines / inch,
A flexographic printing method, wherein a printing speed at the time of printing is 10 to 80 m / min.